irb(main):001:0> class Stunden
irb(main):002:1>   def each
irb(main):003:2>     i = 0
irb(main):004:2>     while i < 12
irb(main):005:3>       yield(i += 1)
irb(main):006:3>     end
irb(main):007:2>   end
irb(main):008:1> end
=> nil
irb(main):009:0> s = Stunden.new
=> #<Stunden:0x40212760>
irb(main):010:0> s.each do |h| print h end
123456789101112=> nil
irb(main):011:0> include Enumerable
=> Object
irb(main):012:0> s.select do |h| h % 2 == 0 end
=> [2, 4, 6, 8, 10, 12]